全文获取类型
收费全文 | 6747篇 |
免费 | 1453篇 |
国内免费 | 1266篇 |
专业分类
化学 | 5300篇 |
晶体学 | 224篇 |
力学 | 437篇 |
综合类 | 99篇 |
数学 | 802篇 |
物理学 | 2604篇 |
出版年
2024年 | 26篇 |
2023年 | 208篇 |
2022年 | 345篇 |
2021年 | 316篇 |
2020年 | 392篇 |
2019年 | 373篇 |
2018年 | 310篇 |
2017年 | 288篇 |
2016年 | 348篇 |
2015年 | 397篇 |
2014年 | 421篇 |
2013年 | 535篇 |
2012年 | 626篇 |
2011年 | 600篇 |
2010年 | 418篇 |
2009年 | 400篇 |
2008年 | 491篇 |
2007年 | 441篇 |
2006年 | 363篇 |
2005年 | 346篇 |
2004年 | 219篇 |
2003年 | 204篇 |
2002年 | 204篇 |
2001年 | 190篇 |
2000年 | 164篇 |
1999年 | 134篇 |
1998年 | 92篇 |
1997年 | 88篇 |
1996年 | 100篇 |
1995年 | 75篇 |
1994年 | 64篇 |
1993年 | 52篇 |
1992年 | 42篇 |
1991年 | 27篇 |
1990年 | 32篇 |
1989年 | 24篇 |
1988年 | 17篇 |
1987年 | 14篇 |
1986年 | 15篇 |
1985年 | 11篇 |
1984年 | 12篇 |
1983年 | 14篇 |
1982年 | 6篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 4篇 |
1978年 | 2篇 |
1973年 | 3篇 |
1957年 | 2篇 |
1936年 | 1篇 |
排序方式: 共有9466条查询结果,搜索用时 125 毫秒
961.
962.
Xia CuiGuang-wei Yuan Jing-yan Yue 《Journal of Computational and Applied Mathematics》2011,236(2):253-264
A nonlinear iteration method named the Picard-Newton iteration is studied for a two-dimensional nonlinear coupled parabolic-hyperbolic system. It serves as an efficient method to solve a nonlinear discrete scheme with second spatial and temporal accuracy. The nonlinear iteration scheme is constructed with a linearization-discretization approach through discretizing the linearized systems of the original nonlinear partial differential equations. It can be viewed as an improved Picard iteration, and can accelerate convergence over the standard Picard iteration. Moreover, the discretization with second-order accuracy in both spatial and temporal variants is introduced to get the Picard-Newton iteration scheme. By using the energy estimate and inductive hypothesis reasoning, the difficulties arising from the nonlinearity and the coupling of different equation types are overcome. It follows that the rigorous theoretical analysis on the approximation of the solution of the Picard-Newton iteration scheme to the solution of the original continuous problem is obtained, which is different from the traditional error estimate that usually estimates the error between the solution of the nonlinear discrete scheme and the solution of the original problem. Moreover, such approximation is independent of the iteration number. Numerical experiments verify the theoretical result, and show that the Picard-Newton iteration scheme with second-order spatial and temporal accuracy is more accurate and efficient than that of first-order temporal accuracy. 相似文献
963.
964.
以湖南电视台和北京卫视为代表,对全国30家电视台卫星频道2008全年日收视率进行时间序列分析,建立了四种拟合模型.其中,大部分电台收视率具有长期趋势或长期趋势和季节效应的综合影响,分别建立ARIMA模型和乘积季节模型,并进行预测,其结果表明模型拟合效果较好. 相似文献
965.
有理对称矩阵的准正交相似 总被引:1,自引:0,他引:1
滕冬梅 《数学的实践与认识》2011,41(18)
对一个有理对称矩阵A,用线性代数的理论直接证明了存在准正交矩阵P使得P~(-1)AP成为A的有理标准形,并给出了P的算法. 相似文献
966.
Long MJ Pan Y Lin HC Hedstrom L Xu B 《Journal of the American Chemical Society》2011,133(26):10006-10009
On the basis of the high affinity binding of trimethoprim (TMP) to Escherichia coli dihydrofolate reductase (eDHFR), TMP-decorated iron oxide nanoparticles bind to eDHFR with high affinity and specificity, which allows magnetic modulation of focal adhesion of mammalian cells adhered to a surface. Besides being the first example of nanoparticles that selectively bind to eDHFR, the biocompatibility of the conjugate of TMP-iron oxide nanoparticles renders a convenient and versatile platform for investigating the cellular responses to specific, mechanical perturbation of proteins via a magnetic force. 相似文献
967.
Sun Z Kim JH Zhao Y Bijarbooneh F Malgras V Lee Y Kang YM Dou SX 《Journal of the American Chemical Society》2011,133(48):19314-19317
Controlling the morphology and size of titanium dioxide (TiO(2)) nanostructures is crucial to obtain superior photocatalytic, photovoltaic, and electrochemical properties. However, the synthetic techniques for preparing such structures, especially those with complex configurations, still remain a challenge because of the rapid hydrolysis of Ti-containing polymer precursors in aqueous solution. Herein, we report a completely novel approach-three-dimensional (3D) TiO(2) nanostructures with favorable dendritic architectures-through a simple hydrothermal synthesis. The size of the 3D TiO(2) dendrites and the morphology of the constituent nano-units, in the form of nanorods, nanoribbons, and nanowires, are controlled by adjusting the precursor hydrolysis rate and the surfactant aggregation. These novel configurations of TiO(2) nanostructures possess higher surface area and superior electrochemical properties compared to nanoparticles with smooth surfaces. Our findings provide an effective solution for the synthesis of complex TiO(2) nano-architectures, which can pave the way to further improve the energy storage and energy conversion efficiency of TiO(2)-based devices. 相似文献
968.
Dan Su Yonggui Song Lulu Geng Binbin Wei Pu Xie Yue Qi Chao Ma Shilin Yang Kaishun Bi Xiaohui Chen 《Chromatographia》2011,73(11-12):1189-1195
In order to provide useful information for rational drug design, the ocular pharmacokinetics of l-carnosine (CAR) and its acetylized prodrug N-acetyl-l-carnosine (NAC) were investigated. The in vivo microdialysis sampling coupled with ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS-MS) was developed for continuously simultaneous monitoring of CAR and NAC in rabbit aqueous humor. The measured in vitro recoveries of the probe were 61.3% for CAR and 65.8% for NAC, while in vivo recoveries decreased to 43.1% for CAR and 43.0% for NAC, respectively. The method was sensitive with LLOQ 20.5 ng mL?1 for CAR and 20.4 ng mL?1 for NAC. The initial data indicated that the value of C max and AUC(0?C??) of NAC were higher than these of CAR (C max 2305 vs. 1,802 ng mL?1), (AUC(0?C??) 1,337 vs. 1,891 ng h mL?1), which indicated that the NAC exhibited better ocular bioavailability and duration. The method was rapid, specific and sensitive for continuously monitoring of aqueous humor and it was successfully applied to pharmacokinetic studies of CAR and NAC. 相似文献
969.
Jing Ning Ying‐Tong Di Shi‐Fei Li Zhao‐Liang Geng Hong‐Ping He Yue‐Hu Wang Yuan‐Yuan Wang Yan Li Shun‐Lin Li Xiao‐Jiang Hao 《Helvetica chimica acta》2011,94(3):376-381
A phytochemical investigation of Toona ciliata var. ciliata afforded three new polyynes, 1 – 3 . Their structures were elucidated on the basis of spectroscopic analysis and chemical methods. Only compound 3 exhibited potent cytotoxicity against the HL‐60 cell line with an IC50 value of 6.7±0.27 μM . 相似文献
970.
Xi‐Bin Xiao Yue‐Xing Lin Geng‐Bo Xu Xu‐Bo Gong Ying Gu Jie‐Feng Tong Jing Yang 《Helvetica chimica acta》2011,94(9):1594-1599
Two new alkaloids, mappine A ( 1 ) and mapposidic acid ( 2 ), together with eleven known compounds, were isolated from the stems of Mappianthus iodoides Hand.‐Mazz. Their structures were elucidated by means of spectroscopic and mass‐spectrometric analyses, particularly 1D‐ and 2D‐NMR spectroscopy. The cytotoxic activities of the two new alkaloids were also evaluated. 相似文献